This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-225734, filed Jul. 26, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cathode ray tube apparatus, and more particularly to a cathode ray tube having an electron gun structure for performing dynamic astigmatism-correction mounted thereon.
2. Description of the Related Art
In general, a color cathode ray tube apparatus is provided with an inline type electron gun structure for emitting triple electron beams, and a deflecting yoke for generating a deflection magnetic field for scanning on a phosphor screen in a horizontal direction and a vertical direction by deflecting the electron beams emitted from the electron gun structure. This deflecting yoke forms a non-uniform magnetic field by a pin cushion type horizontal deflection magnetic field and a barrel type vertical deflection magnetic field.
The electron beams having passed through such a non-uniform magnetic field are affected by deflection aberration, i.e., astigmatism included in the deflection magnetic field. Therefore, a beam spot of the electron beams which have reached a periphery part of the phosphor screen is over-focused in the vertical direction by deflection aberration, which results in blur in the vertical direction and lateral collapse wide in the horizontal direction. The deflection aberration which affects the electron beams becomes larger as a dimension of the tube is increased and a deflection angle becomes wider. Such distortion of the beam spot considerably deteriorates the resolution of the periphery part of the phosphor screen.
As means for solving deterioration of the resolution caused due to the deflection aberration, there is such an electron gun structure as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 61-99249. This electron gun structure is provided with first to fifth grids and forms an electron beam generation portion, a non-axial-symmetrical lens, and a final main focus lens along a traveling direction of the electron beams. The non-axial-symmetrical lens is formed by providing three non-axial-symmetrical electron beam passage holes on each of opposed surfaces of electrodes adjacent to each other.
This electron gun structure reduces the influence of the deflection aberration of the deflection magnetic field given to the electron beams which are deflected around the phosphor screen and corrects the distortion of the beam spot by changing lens intensities of the non-axial-symmetrical lens and the final main lens in synchronization with a change in the deflection magnetic field.
In such an electron gun structure, however, when the electron beams are defected around the phosphor screen, the influence of the deflection aberration of the deflection magnetic field is extremely large. Further, even if the blur of the beam spot can be eliminated, the lateral collapse can not be sufficiently corrected.
Furthermore, as another means for solving deterioration of the resolution caused due to the deflection aberration, there is proposed such a dynamic focusing type electron gun structure as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 64-38497.
This electron gun structure constitutes a final main focus lens by a dynamic focus electrode to which a dynamic focus voltage is applied, an anode electrode to which an anode voltage is applied, and an auxiliary electrode arranged between these electrodes. To the auxiliary electrode is supplied a voltage obtained by subjecting the anode voltage to resistance division by using a resistor arranged in the vicinity of the electron gun structure.
As a result, each non-axial-symmetrical lens is formed between the dynamic focus electrode and the auxiliary electrode and between the auxiliary electrode and the anode electrode. When the dynamic focus voltage is applied to the dynamic focus electrode according to deflect the electron beams in the periphery part of the phosphor screen, the final main focus lens including the non-axial-symmetrical lens generates the lens action for divergence only in the vertical direction without producing the lens action in the horizontal direction.
This electron gun structure corrects the distortion of the electron beam spot in the periphery part of the phosphor screen by such a lens action.
In such an electron gun structure, however, an alternating component of the dynamic focus voltage is superposed on the applied voltage of the auxiliary electrode by the electrostatic capacity between the electrodes constituting the final main focus lens by applying the dynamic focus voltage to the dynamic focus electrode. As a result, the non-axial-symmetrical lens formed between the dynamic focus electrode and the auxiliary electrode lacks the lens action, and an undesired lens action is generated to the non-axial-symmetrical lens formed between the auxiliary electrode and the anode electrode.
Therefore, the distortion of the beam spot can not be sufficiently corrected in the periphery part of the phosphor screen, and the excellent focusing characteristic can be hardly obtained in the entire phosphor screen area.
In order to obtain the excellent focusing characteristic in the entire phosphor screen area, the distortion of the beam spot must be corrected in the periphery area of the phosphor screen. Moreover, it is necessary to reduce a superposition ratio of the alternating component of the dynamic focus voltage to the auxiliary electrode and form the sufficient lens action to the lens for compensating the influence of the deflection aberration to the electron beams.
In view of the above-described problems, it is an object of the present invention to provide a cathode ray tube apparatus capable of forming a beam spot having an excellent shape across an entire phosphor screen area.
According to the present invention, there is provided a cathode ray tube apparatus comprising:
an electron gun structure having an electron beam formation portion for forming electron beams and a main lens portion for focusing the electron beams on a phosphor screen; and
a deflection yoke for generating a deflection magnetic field for scanning in a horizontal direction and a vertical direction on the phosphor screen by deflecting the electron beams emitted from the electron gun structure,
wherein the electron gun structure includes a first non-axial-symmetrical lens portion whose lens action changes in accordance with a quantity of deflection of the electron beams and which is arranged in the vicinity of the electron beam formation portion and a second non-axial-symmetrical lens portion whose lens action changes in accordance with a quantity of deflection of the electron beam and which is formed to the main lens portion;
the first non-axial-symmetrical lens portion has a lens action in the vertical direction by which a focusing action relative to the electron beams is strengthened as a quantity of deflection of the electron beams increases and a lens action in the horizontal direction which substantially rarely acts on the electron beams as compared with the lens action in the vertical direction; and
a comprehensive lens system of the second non-axial-symmetrical lens portion and the main lens portion has a lens action in the vertical direction by which a divergence action relative to the electron beams is strengthened as a quantity of deflection of the electron beams increases and a lens action in the horizontal direction which substantially rarely acts on the electron beams relatively.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.